Vitamin B-6 Requirement and Oral Contraceptive Use—A Concern?

Abstract

There has been increasing concern as to whether oral contraceptives (OCs) increase the requirements for certain vitamins including vitamin B-6. The over 60 research studies on this relationship have used 2 parameters to evaluate vitamin B-6 status: 1) direct measures of vitamin B-6 metabolism and 2) indirect measures such as tryptophan metabolite excretion erythrocyte aminotransferase activity and stimulation and methionine metabolite excretion. Initial studies of the effect of OCs on vitamin B-6 status concentrated on altered tryptophan metabolism but there has been a recent trend toward evaluation of other indices. If only xanthurenic acid excretion is used as a criterion of OC effects the data generally suggest that OC users require supplementary B-6. Conversely analysis of plasma pyridoxal 5-phosphate (PLP) indicates such supplementation is not necessary. This points to the need for researchers to take into account the parameters that were used in presenting their findings. The observation of abnormal tryptophan is unique in that results of other tests such as the methionine load do not indicate that OC use is associated with an abnormal vitamin B-6 status. Although there may be slightly more PLP within cells where transanimase activity is elevated indicating a slightly greater need for vitamin B-6 the body appears to deal with this need by drawing on circulating PLP levels. The plasma levels of PLP in OC users are not deficient suggesting that the nutriture of OC users is not compromised.